I learned how to say “no” to outrageous demands on my time, to companies which asked that I give it all in return for some meager equity grant that could be worth millions but more likely not worth the paper it was written on.
Fairly boring, really, but not covered in my CS or liberal arts studies in college.
You get so caught up in the moment: get a job, make money, pay your debts, you don't get a chance to step back and ask what you want out of life.
I've tried working with startups again since I left that world, and I always end up leaving after a few months to a year. Most startups are managed as though everything is a crisis, your hair is on fire all the time (and if it's not, then clearly you're doing something wrong). Firms, capital back companies are not new. Digital technology and communications remove a lot of the friction, but a lot of the corporate politics you find in today's hot startup existed in the 1990s, 1980s, 1970s and so on. It's not just a failure to learn from the past, it's an outright refusal, the constant "it'll be different this time" mantra.
Surprise: it's pretty much the same shit, different logos and domain names (and apps).